Watermelon: Benefits, Nutrition, Lycopene and Citrulline

Watermelon is a large, sweet melon that is about 91% water by weight, and a cup of diced watermelon has about 46 calories in USDA data. Its red flesh is one of the richest common food sources of lycopene, the same red pigment found in tomatoes, and it contains citrulline, an amino acid named after the watermelon itself. This guide covers watermelon nutrition from the USDA database, what human trials found about watermelon benefits, how the seeds and rind compare, and the CDC advice on keeping cut melon safe.

Peptide Labs does not sell watermelon or watermelon products. This article is general nutrition information, not medical advice.

Watermelon nutrition facts

In USDA SR Legacy data (Watermelon, raw, FDC 167765), watermelon is mostly water and natural sugar, with modest amounts of vitamin C, vitamin A and potassium and very little fiber, fat or protein. Here is what common servings provide:

Because it is so watery, watermelon has fewer calories per cup than many fruits, but its sugar comes with little fiber. For comparison, a cup of cantaloupe cubes has 54 calories with far more vitamin A and vitamin C in USDA data; see our cantaloupe guide, our guide to fruit sugar levels and our low glycemic foods guide.

Water content and hydration

USDA lists 91.45 grams of water per 100 grams of raw watermelon, so a wedge holds roughly a cup of water, along with some potassium. It is not a sports drink, though: USDA lists only about 1 milligram of sodium per 100 grams. Our electrolytes guide explains when sodium and other electrolytes matter, and our guide to potassium in food lists richer sources.

Lycopene in watermelon

Lycopene is a red carotenoid pigment. USDA lists about 4,500 micrograms of lycopene per 100 grams of raw watermelon, compared with about 2,600 micrograms per 100 grams of raw red tomatoes. Studies of tomato products show heat processing helps lycopene absorption, but watermelon is eaten raw, so researchers asked whether the body absorbs it well.

A 2003 crossover study in 23 healthy adults on controlled diets found that fresh-frozen watermelon juice raised blood lycopene and beta-carotene levels, and that blood lycopene after three weeks did not differ from a tomato juice period. It was a small, short study of blood levels, not of health outcomes. Our lycopene guide covers what research on lycopene does and does not show.

Citrulline in watermelon

Citrulline is an amino acid used in the body’s nitric oxide system, which helps blood vessels relax, and watermelon is a rich natural source of it. A 2005 laboratory analysis found citrulline in every watermelon tested, at similar levels in seeded and seedless types. The rind held more citrulline than the flesh on a dry-weight basis but slightly less per gram of fresh fruit, so eating the rind is not a shortcut to much more. Our L-citrulline guide covers the supplement form, and our beetroot guide covers dietary nitrate, another route the body uses to make nitric oxide.

Watermelon benefits: what the research shows

Human trials of watermelon are few and small, and several reviews pool watermelon with citrulline supplements, which makes the fruit’s own effect hard to isolate:

• Blood pressure and lipids: a 2023 meta-analysis of 9 randomized trials found watermelon lowered systolic blood pressure, total cholesterol and LDL, but also found fasting blood sugar went up, and saw no significant change in diastolic pressure, heart rate, BMI or body fat. The authors said results should be used with caution.
• Older adults: a 2025 meta-analysis of 15 trials with 415 middle-aged and older people pooled citrulline supplements and watermelon together and reported average drops of about 4 mmHg systolic and 2.5 mmHg diastolic. Most of the data came from supplements.
• Blood vessel function: a 2025 review of 8 trials in 176 people found citrulline supplements improved flow-mediated dilation, a test of artery widening, while artery stiffness did not change significantly.

The honest summary: watermelon is a hydrating, low-calorie fruit with lycopene and some vitamin C, and the research on blood pressure is early and mostly built on supplements. It is not a substitute for blood pressure care, and claims that watermelon works like a prescription drug are not supported.

Watermelon seeds and rind

The black seeds of seeded watermelons can be swallowed, and dried, shelled seed kernels are sold as a snack. USDA lists dried watermelon seed kernels very differently from the flesh, as a calorie-dense seed:

The pale soft seeds in seedless watermelons are eaten with the flesh. The white part of the rind is edible and is pickled or stir-fried in many cuisines; scrub the outside well first.

Keeping cut watermelon safe

Melons grow on the ground, and germs on the rind can be carried into the flesh by a knife. CDC has linked pre-cut melon to Salmonella outbreaks: in 2018, pre-cut watermelon, honeydew, cantaloupe and fruit mixes from one company sickened 77 people in 9 states, 36 of them hospitalized, and in 2019 pre-cut melon from the same company was linked to 137 illnesses in 10 states, with 38 hospitalized.

• Scrub the rind: FDA advises scrubbing firm produce such as melons with a clean produce brush under running water before cutting, even though you do not eat the rind. Soap and produce washes are not recommended.
• Refrigerate cut melon: CDC advises against eating cut melon left out more than 2 hours, or 1 hour when it is hotter than 90 degrees Fahrenheit, such as at a picnic.
• Use it within a week: CDC also advises against eating cut melon kept in the refrigerator for more than a week.
• Higher-risk groups: CDC names pregnant people, newborns, adults 65 or older and people with weakened immune systems as most at risk from Listeria, so freshly cut melon is the safer choice for them.

Watermelon is not one of the nine major food allergens on US labels, but any food can cause a reaction; seek urgent care for swelling or breathing trouble. For a deeply colored fruit with more fiber, see our guide to blueberries, and our vitamin C foods guide lists fruits richer in vitamin C.

Frequently Asked Questions

Questions about a label? Contact us or read our Buyer’s Guide. Food comes first; follow the label and ask a healthcare provider before starting a supplement, especially if you take medicines, are pregnant or have a food allergy. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Last reviewed October 2026.

Related guides: Blueberries: Nutrition, Benefits and Frozen Blueberries, Honeydew Melon: Benefits, USDA Nutrition and Food Safety, Cantaloupe Benefits: USDA Cantaloupe Nutrition, Calories and Safety, Types of Melons: Muskmelon Groups, Casaba, Canary and USDA Values.